The present invention relates to semiconductor device fabrication and integrated circuits and, more specifically, to structures for printing patterns and methods of forming printed patterns.
Lithography techniques, such as optical proximity correction (OPC), may be used in an attempt to alleviate mask transfer problems. In OPC, non-printing dummy assist features, also known as sub-resolution dummy assist features (SRAFs), are placed on the photomask pattern to enhance the printability of the main features on the photomask pattern. Because SRAF's are non-printing, these dummy assist features of the photomask are not replicated in a photoresist on a wafer.
As pitch shrinks, the aspect ratio of depth to width for a line/space (L/S) pattern increases. With the increased aspect ratio, the risk of pattern collapse during either lithography or etching increases. This increased risk of pattern collapse can be offset by reducing the thickness of the photoresist and/or the thickness of the film being etched in order to reduce the aspect ratio. However, etch selectivity suffers with such thickness reductions.